Aspects of the Astrophysics and Nuclear Physics of r-Process Nucleosynthesis Rebecca Surman Union College Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology July 2008

r-process nucleosynthesis R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 2/25

r-process nucleosynthesis - current challenges Astrophysics The astrophysical site(s) not conclusively known; possibilities include: • core collapse supernovae e.g., Meyer et al (1992), Woosley et al (1994), Takahashi et al (1994) • neutron star mergers e.g., Meyer (1989), Frieburghaus et al (1999), Rosswog et al (2001) • shocked surface layers of O-Ne-Mg cores e.g., Wanajo et al (2003), Ning et al (2007) • gamma-ray bursts e.g., Surman et al (2005) Nuclear Physics Nuclear properties for ~3000 nuclei far from stability nuclear masses fission probabilities, distribution of fragments beta decay rates neutron capture rates (?) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 3/25

halo star observations Cowan et al (2006) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 4/25

halo star observations Main r process Cowan et al (2006) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 5/25

halo star observations Weak r process Main r process core collapse supernovae ? Cowan et al (2006) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 6/25

the SN neutrino-driven wind Important parameters  outflow timescale entropy electron fraction shock PNS  p, n  4He + n  seed nuclei + n  r process R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 7/25

the main r process How is a consistent pattern achieved? Ye = 0.25 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 8/25

Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) low Ye main r process Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 9/25

Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) low Ye main r process Fission Cycling Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 9/25

Surman, Beun, McLaughlin, Kane, & Hix, J Phys G 35, 014059 (2008) fission cycling and the neutrino luminosities (1051 erg/s) (1051 erg/s) Surman, Beun, McLaughlin, Kane, & Hix, J Phys G 35, 014059 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 10/25

Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) fission cycling: comparison with halo star data Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 11/25

fission cycling and the main r process In the SN neutrino-driven wind, the electron neutrino flux determines whether a successful r process is possible The electron neutrino flux can be reduced by:  fast outflow  active-sterile neutrino oscillations  other new physics If a sufficient reduction in the electron neutrino flux occurs, fission cycling may insure a stable abundance distribution consistent with the pattern in metal-poor halo stars Accurate fission probabilities and fragment distributions are required to correctly predict the details of the final abundance distribution for a fission cycling main r process. R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 12/25

black hole - neutron star merger Orbit of a black hole - neutron star binary decays by gravitational wave emission Tidal disruption of the neutron star produces a rapidly accreting disk around the black hole (AD-BH)  possible engine for a short gamma-ray burst animation credit: NASA/SkyWorks Digital R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 13/25

PNS – AD-BH comparison jet (?) shock outflow  PNS BH  accretion disk R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 14/25

PNS – AD-BH nuclear physics nucleosynthesis jet jet (?) shock nucleosynthesis outflow  PNS BH  accretion disk neutrino scattering and emission nuclear physics of disk nuclear physics of core R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 15/25

3D black hole - neutron star merger model 1.6 M neutron star + 2.5 M black hole with a = 0.6 Evolved until remains of neutron star form an accretion disk Model by M. Ruffert and H.-Th. Janka R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 16/25

Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 neutrino temperatures Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 17/25

Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 our nucleosynthesis calculation Outflow parameterization Adiabatic flow with velocity as a function of radial distance: with v ~ 104 km/s, 0.2 < < 1.4, 10 < s/k < 50 Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 18/25

Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 sample nucleosynthetic outcomes All trajectories from the inner disk region make r-process nuclei This is a direct consequence of the neutrino physics Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 19/25

sample nucleosynthetic outcomes Example: the importance of beta decay rates Möller et al (2003) Möller et al (1997) Möller et al (2003) + exp R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 20/25

neutron capture rates and the r process Do they make any difference? can influence time until onset of freezeout e.g., Goriely (1997,8), Farouqi et al, Rauscher (2005) can shape local details of the abundance distribution e.g., Surman et al (1998), Surman & Engel (2001) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 21/25

Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 mass model - neutron capture rate comparison Neutron capture rate variation Mass model variation Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 22/25

Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 nonequilibrium effects of individual capture rates 130 peak rare earth region + 195 peak Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 23/25

Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 influential neutron capture rates Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 Capture rates that affect a 5-40% change in the global r-process abundance pattern for increases to the rate by a factor of: 10 50 100-1000 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 24/25

summary We still don’t know where the r process takes place  evidence increasingly points to core collapse supernovae for the site of the main r process (fission cycling would help)  list of potential sites should include hot outflows from black hole-neutron star mergers, particularly for the weak r process Everybody knows we need nuclear masses and beta decay rates  individual neutron capture rates are also important  fission probabilities and fragment distributions may be crucial R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 25/25